Two-sided electron-sensitive screen



March 31, 1953 Hl B. LAw 2,633,547

TWO-SIDED ELECTRON-SENSITIVE SCREEN Filed June 50, 1950 Puff ya ,W4/M6 VVV/1550 q @MAL 31.55 me@ Mlm, J/a/m 1, j;

55p v/ 0 W76 INVENTOR /mldlaw ATTORNEY Patented Mar. 31, 1953 TWG-SIDED ELECTRON-'SENSITIVE SCREEN Harold B. Law, Princeton, N. LI., assignor to "Radio Corporation of America, aicorporation of Dela- Application June 30, 1950, SerialNo. 171,394

Claims. (Cl.f31'3--'92i) This invention `relates tocathode-ray tubes and particularly .to improvements in 'two-sided. .electron-sensitive screens or targets -for such tubes.

It has previously been vproposed .to derive signals from the rear surface of a cathode-ray screen :and to .utilize said .signais l*for controlling theiocus .or the .timing of the beam, :or for securi-ng linear, vertical, radial .or other directional scanning :movements of a high order of precision. .By Wayof example, rZworykin in U S. Patent .2,415,059 shows a color-kinescope having .a screen made 4up or" a multiplicity .of groups-ofthree .phosphor coated lines, .each capable of emitting light of a diierent color, land three photocells, at the rear of the screen, eachsensitive to vone of the colors emitted 'by the colorphosphor lines. The control signals generated by `the photocells are employed to accelerate or decelerate .the deflection yof the beam rin accordance with its .departure from .the phosphor-line being scanned. The control signals thus serve to restore the instantaneous line-deiiection path of the scanning beam on that `phosphor line. Obviously, the amplitude of the control signals lin ZWorykins color-kinescope is a function of the intensity of the lights which the photocells pick up from the rear of its screen. It will .therefore be apparent that when any portion or the televised scene contains .a .relatively dark area, only very Weak photo-electric signals are available for control purposes. Accordingly, the principal object of the present invention is to provide an .improved "twosided electron-sensitive screen of the general character described, and one characterized by the increased intensity of the light, available for control purposes, adjacent to its rear surface,

Another and important object of the present invention is to achieve said principal object Without any substantial `diminution in the intensity of the fluorescent llight ernanatingjirom the obverse face of said screen, or any increase in the length and Width dimensions of the screen.

Still another object of the present invention is to provide an improved color-'image tube of the kind wherein the beam is subjected to 'vernier-control signals derived from the rear surface of its screen, and one wherein said control signals are derived from a fast phosphor Whose color i-s unimportant from the standpoint of image rendition. 'l IStated generally, the foregoing objects are achieved in accordance vwith the invention by the provision of an electron-sensitive target comprising an electron-transparent light-reflecting layer having any desired pattern of color-phosphor materials on its obverse face -and a Vdiscrete electron-transparent signal emissive phosphor material of the desiredcolor-emissive and light-decay characteristics -on its opposite Vor 'rear surface. The light emitted by impact of the electronbeam is 'reflected rearwardlyby the light-reiiecting layer 'and is picked-up, Aas'by a photocell, and the resulting signals used, as `before,'to control the focus `or timing of the beam. Since the light emitted by said signal-generating phosphor layer is reflected rearwardly, Yand :is not visible from the iront -of vthe tube, it :may'have color and decay lcl'iaracteristics other than that of y'the phosphor or phosphors on VVthe obverse face of the screen. When the Atube Iin which the screen is contained is vof the color-kinesc'ope variety the velocity `of the Ibeam varies with 'the light and shade of the scene being televised. Thus if a bright area is to appear on the screen the intensity of the beam is -quite high so that is passes through the electron-transparent signal-generating vand light-renecting areas and activates the picture-generating phosphor or phosphors on the vobverse surface of the light `reiiecting layer. On the other Yhand if a dark picture-area is indicated (by the video signal) the intensity of the beam is made suiicient merely to actuate the signal-generating phosphor indicia on the rear of the screen. Thus, contrary tothe usual practice, control signals are available irrespective of the instantaneous-degree of 'light and shade of the televised image.

The invention is described in greater detail 'in connection with the accompanying single sheet of drawings, wherein,

Fig. l is a partly diagrammatic view of a tele vision receiving system employing Va color-kinescope having a two-sided screen constructed in accordance with the principle of the present invention and,

Fig. 2 is a partial sectional view of 'the "screen of Fig. 1. l A l In the `drawing the invention is shown applied to cathode-ray tube of the vcolor-innescope varie'ty. The tube here shown 'is oi conventional shape and dimensions and 'comprises an evacuated glass venvelope having a main chamber in the form of -a tru-sturm I, which contains the eiectron-sensitive screen 3 (later described) -`Aanti-a neck portion -Ei containing the cathode rl, grid y9 and first anode il ci an electron gun.

The frustuin of the envelope contains a hermetically sealed port orl'ens it through which light, emanating from the rear surface oi the screen 3, passes to a photocell I5 on the outside of the envelope. As is conventional, the envelope also contains an accelerating electrode or second anode in the form of a conductive coating i1 on the inner surface of the main chamber I and neck 5. As is also conventional, horizontal and vertical magnetic deecting coils I9 and 2I are provided on the neck of the tube for imparting the requisite screen-scanning movements to the electron beam (not shown).

In the embodiment of the invention which has been selected for illustration the target or screen 3 comprises a glass or other transparent foundation 23, which is provided on its rear face with a multiplicity of groups-of-three phosphor lines R, B and G extending in a direction perpendicular to the direction of line scanning. Each line is constituted of a phosphor material capable of emitting light of a particular color component When struck by the beam emanating from the gun of the tube.

As taught by Leverenz in U. S. Patent 2,310,863 when the phosphor lines which make up the different groups are to emit blue, green and red light, respectively, the materials of which the lines are composed may comprise: Silveractivated zinc sulfide and zirconium silicate for the blue lines B. Alpha-Willemite activated with manganese or zinc cadmium sulde activated with silver for the green lines G. Chromiumactivated aluminum berylliate or zinc cadmium sulfide activated by silver for the red lines R.

The phosphor layers R, B, and G, here illustrated, extend in unbroken lines from the bottom to the top of the transparent foundation plate 23. They may however be made up of a multiplicity of phosphor dots of sub-elemental image dimensions and, in either event, may extend horizontally across the screen, if desired. They may be applied to the foundation 23 in any convenient manner, e. g. by means of a "silk-screen (not shown), a spray-gun and mask (not shown) or by a conventional "settling process, from a liquid suspension of phosphor particles.

After the three color-phosphors R, B, and G have all been laid down on the foundation 23, an electron-transparent light-reecting layer 25, preferably of aluminum, is laid down on top of the phosphor lines vor dots as by a conventional evaporation process, in vacuo. Thereafter the electron-transparent signal-generating lines 21 or other indicia are laid down, as through a mask, not shown, on top of the light-reilecting layer 25 in register with the underlying picturegenerating phosphor areas. In the instant case but one signal-generating line 21 is used for each group-of-three picture-generating lines R, B, G. These extremely thin signal-generating lines 21 are preferably constituted of zinc oxide or other fast phosphor, i. e. one having a rapid light decay-characteristic. The color of the light emitted by the signal-generating phosphor 21 is immaterial where but one signal-generating line or area is used for each group-of-three picturegenerating phosphor areas.

If more than one signal generating phosphor is employed they should exhibit different coloremissive characteristics. In such an embodiment of the invention, separate photocells (not shown) are employed to. pick-up the different color-signals, as in the Zworykin patent.

When the concentration of the phosphor particles which make up the picture-generating lines R, B and G is the same, green phosphor will ordinarily emit light of an intensity greater than that of the colored lights emitted by the blue and red phosphors. Hence When the signalgenerating phosphor layer 21 is placed in register with the green phosphor G no serious or even noticeable attenuation in the colored image results from the passage of the 'beam through the electron-transparent layers 25 and 21.

The circuit shown in Fig. l for utilizing the signals generated by the impress of light from the rear of the screen 3 upon the light-sensitive device I5 forms no part of the present invention and in fact is a duplicate of the circuit claimed by Paul K. Weimer in copending application Serial No. 5,431, iiled January 30, 1948, now Patent No. 2,545,325. Here the output of the photocell or other suitable light-sensitive device I5 is applied to a signal clipper 29 which takes out variations in the intensity of the light resulting from the variations in the video signals, which are applied to the grid 9 of the tube. The pulses of constant amplitude, derived from the signal clipper 29 are applied to a pulse delay line 3l which operates, in timed sequence, through ampliers 33, 35 and 31 to trigger on switches 34, 3B, 38 which pass the green, blue and red video-signals, to the grid 9 of the tube.

In conclusion it should be noted that the synchronizing signal maintains its control so long as there is light output from the signal-generating zinc oxide coatings 21. Thus, control is maintained even when the picture-generating phosphor areas G are down to black level due to the attenuation of the beam in the zinc oxide and aluminum layers.

What is claimed is: f

l. An electron-sensitive color target comprising a foundation having a multiplicity of groups of phosphor-coated elemental areas on a surface thereof, said elemental areas each being constituted essentially of a phosphor material capable of emitting light of a color individual to that area, an electron-transparent light-reflecting metal layer supported upon said groups of phosphor coated areas, and a plurality of discrete electron-transparent phosphor coatings disposed on said metal layer each in register with a particular one of the elemental color-phosphor areas of each group.

2. The invention as set forth in claim 1 and wherein each of said electron-transparent phosphor coatings comprises a phosphor material capable of emitting light of a color corresponding to that of the light emitted by the phosphor coated area with Which said transparent-coating is in register.

3. The invention as set forth in claim l and wherein the phosphor material of which one of said elemental areas is comprised is of a type that normally emits colored light of an intensity greater than that of the intensity of the colored lights emitted by the phosphor materials o1" the other elemental areas, and wherein said electrontransparent phosphor coatings are vdisposed in register with the elemental areas of said greater light intensity characteristic.

4. The invention as set forth in claim i and wherein said discrete electron-transparent phosphor coatings are constituted essentially of a phosphor material having a light-decay characteristic which is rapid as compared to the lightdecay characteristics of the phosphor materials of which said phosphor-coated elemental areas are comprised.

5. The invention as set forth in claim 4 and HAROLD B. LAW.

REFERENCES CITED The following references are of record in the file of this patent:

Number 6 UNITED STATES PATENTS Name Date Schlesinger Feb. 4, 1936 Van Steenis Dee. 10, 1940 Law Dec. 1, 1942 FondaJ July 15, 1947 Shredder Aug. 3, 1948 Henderson Aug. 10, 1948 Huffman Dec. 13, 1949 Koch Mar. 13, 1951 Zworykin Sept. 4, 1951 

